1. Field of the Invention
The present invention relates to a composite substrate, and an elastic wave device using the same.
2. Description of the Related Art
As elastic wave devices, surface acoustic wave devices that can function as filters or resonators for use in, for example, cellular phones, Lamb wave devices or thin film resonators (FEAR: Film Bulk Acoustic Resonator) using a piezoelectric thin film, and the like are known. Surface acoustic wave devices have a structure in which a support substrate and a piezoelectric substrate that transmits a surface acoustic wave wave are bonded to each other and a comb shaped electrode capable of exciting a surface acoustic wave is provided on the front surface of the piezoelectric substrate. Thus, by bonding a support substrate having a coefficient of thermal expansion smaller than that of a piezoelectric substrate to the piezoelectric substrate, changes in the dimension of the piezoelectric substrate caused by the temperature changes are suppressed to thereby suppress changes in the frequency properties as surface acoustic wave devices. For example, Patent Document 1 proposes a surface acoustic wave device having a structure in which an LT substrate (LT is the abbreviation for lithium tantalate) as a piezoelectric substrate and a silicon substrate as a support substrate are bonded to each other with an adhesive layer containing an epoxy adhesive. Such a surface acoustic device is disposed on a ceramic substrate by flip chip bonding through a gold ball, and sealed with a resin. Then, an electrode provided on the rear surface of the ceramic substrate is mounted on a printed-circuit board through a lead-free solder. Such a surface acoustic wave device may be mounted on a ceramic substrate through a ball containing a lead-free solder in place of the gold ball. Also in this case, in a reflow process, the lead-free solder is melted and re-solidified for mounting.
Patent Document 1: JP 2007-150931 A